Urinary Anatomy Phsyiology
Anatomy & Physiology for Health Professions: An Interactive Journey
Second Edition
CHAPTER
17
The Urinary System: Filtration and Fluid Balance
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
Learning Objectives
• Identify the parts of the urinary system. • Explain general functions of the urinary system. • Explain the relationships of the urinary system to the endocrine & circulatory systems. • Describe the structure & function of the nephron
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Learning Objectives
• Compare urinary system of the male with the female urinary system. • Identify the constituents of urine. • Differentiate processes of secretion, filtration, and reabsorption & where they occur in the nephron.
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Introduction
• The urinary system acts as a purification plant, cleaning the blood of waste materials. • Urinary system controls electrolyte and fluid balances for your body. • Kidneys filter blood, reabsorb and secrete ions, and produce urine.
– Without this important function you would die in a few days.
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System Overview
• Consists of:
– 2 kidneys; bean-shaped organs located in the superior dorsal abdominal cavity that filter blood and make urine – Accessory structures – Ureter is a tube that carries urine from each kidney to – The single urinary bladder, located in the inferior ventral pelvic cavity.
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System Overview
• Bladder is basically an expandable sac • Urethra is the tube that transports urine from the bladder to the outside of the body. • The job of the urinary system is to make urine, thereby controlling:
– the body’s fluid and electrolyte balance – eliminating waste products
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System Overview
• To make urine, 3 processes are necessary:
– Filtration – filtering the blood. What passes through the filter is called a filtrate. – Reabsorption – substances stay in the body after being removed from urine – Secretion – substances move from the blood stream and leave the body in the urine
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Figure 17-1
Anatomy of the urinary system.
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External Anatomy of the Kidney
• The kidney is covered by a fibrous layer of connective tissue called the renal capsule.
– Part that gives the kidney it’s bean shape is called the renal hilum.
• At the hilum
– renal arteries bring blood to the kidneys to be filtered – renal veins take the filtered blood away from the kidney. – The ureter is also attached at the hilum to transport urine from the kidney to the bladder.
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Internal Anatomy of the Kidney
• The kidney can be divided into 3 layers:
– Renal cortex – outer layer –this is where blood filtration occurs – Renal medulla – middle layer – contains a number of triangle-shaped, striped areas called renal pyramids
Composed of collecting tubules for the urine that is formed in the kidney
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Internal Anatomy of the Kidney
• The kidney can be divided into 3 layers:
– Renal pelvis – inner layer – a funnel, divided into 2 or 3 large collecting cups called major calyces.
Each major calyx is divided into several minor calyces, forming cup-shaped areas around the tips of the pyramids.
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Internal Anatomy of Kidney
• The blood is filtered by millions of tiny filters in the cortex, • Filtrate flows through tiny tubules in the medulla and collects in the renal pelvis. • Renal pelvis, the enlarged proximal portion of the ureter, empties into the ureter where urine is carried to the bladder.
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Figure 17-2
The internal and external anatomy of the kidney.
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Internal Anatomy of Kidney
• Blood vessels
– Good blood supply to the kidney is essential – A single renal artery enters each kidney at the hilum, branching into 5 segmental arteries. – The segmental arteries branch into lobar arteries in the renal sinus.
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The Nephron
• The functional unit of the kidney is the nephron, consisting of millions of microscopic funnels and tubules. • The nephron can be divided into two distinct parts:
– The renal corpuscle – a filter – The renal tubule – where reabsorption and secretion take place
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Renal Corpuscle
• Blood enters the renal corpuscle via the glomerulus, a ball of capillaries. • Surrounding the glomerulus is a doublelayered membrane called the glomerular capsule, or Bowman’s capsule.
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Renal Corpuscle
• Blood flows into the glomerulus and everything BUT blood cells and a few large molecules, mainly protein, are pushed from the capillaries across the filter and into the glomerular capsule. • The material filtered from the blood into the glomerular capsule is called glomerular filtrate. • If blood or protein leaks into urine it can indicate a kidney filtration problem.
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Figure 17-4
The nephron.
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Renal Tubule
• The rest of the nephron is a series of tubes known as renal tubules. • Glomerular filtrate travels from the glomerular capsule into the first part of the renal tubule, the proximal tubule.
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Renal Tubule
• From the proximal tubule, glomerular filtrate flows into the nephron loop (or the Loop of Henle).
– The nephron loop consists of the descending loop (similar in structure to the proximal tubule) and the ascending loop
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Renal Tubule
• Glomerular filtrate travels from the nephron loop to the distal tubule.
– The wall of the distal tubule is like that of the ascending branch of the nephron loop. – From the distal tubule, glomerular filtrate flows into one of several collecting ducts
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Renal Tubule
• The collecting ducts lead to minor calyces, then to major calyces, the renal pelvis, and the ureter. • At this point, the glomerular filtrate is urine.
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Figure 17-5
A functional renal unit.
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Renal Tubule
• Blood vessels are in close proximity to the nephrons because substances move between the tubules and the bloodstream.
– Blood approaches the nephron via the afferent arteriole. – Blood flows from the afferent arteriole into the glomerulus. – Blood flows from the glomerulus via the efferent arteriole into the peritubular capillaries and vasa recta.
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Renal Tubule
• Blood vessels are in close proximity to the nephrons because substances move between the tubules and the bloodstream.
– These surrounding blood vessels allow for reabsorption and secretion. – Blood leaves the nephron via the cortical radiate veins.
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Clinical Application: Trauma, Ischemia, and Kidney Damage
• The kidney is well vascularized, with each nephron surrounded by blood vessels. • The flow of blood is controlled by the afferent arteriole. • When blood flow decreases for a period of time, oxygen delivery to the nephron decreases and ischemia results.
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Clinical Application: Trauma, Ischemia, and Kidney Damage
• Blood flow can be decreased by any number of hormonal mechanisms causing prolonged vasoconstriction, such as severe blood loss. • If the situation continues long enough, the tissues will become ischemic and eventually die, causing kidney failure that can be temporary or permanent.
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Urine Formation
• The kidney controls fluid and electrolyte balance by controlling urine volume and composition. • In order to form urine, the nephron must perform three processes:
– Glomerular filtration – Tubular reabsorption – Tubular secretion
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Filtration
• During glomerular filtration, fluid and molecules pass from the glomerular capillaries into the glomerular capsule.
– Across a filter composed of the walls of the capillaries and the podocytes of the glomerular capsule – The filtrate flows into the renal tubule where the chemistry is controlled by reabsorption and secretion – Filtration moves fluid and chemicals into the nephron from blood – Glomerular filtrate is chemically similar to blood
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Reabsorption and Secretion
• Urine is chemically different from plasma because reabsorption and secretion control the concentration of chemicals and volume of urine.
– Substances that are reabsorbed pass from the renal tubule into the peritubular capillaries and return to the blood stream. – Substances that are secreted pass through the peritubular capillaries into the renal tubule and eventually leave the body as urine. – Some substances, like glucose, are completely reabsorbed while substances like metabolic waste products (urea and creatinine) are almost completely secreted as urine.
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Figure 17-6
The processes involved in urine formation.
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Table 17-1
Kidney Fluid Chemistry.
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Control of Filtration
• Filtration is controlled by several factors.
– Filter size – determines what gets through the filter
Podocytes and capillary walls of the renal corpuscle create a filter with fixed openings. Plasma, and many of the substances dissolved in plasma, pass through the filter, but blood cells, platelets, and large molecules, can’t get into a healthy kidney.
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Control of Filtration
• Filtration is controlled by several factors.
– Pressure
Higher pressure on one side of the filter allows chemicals to be pushed though the filter more quickly. Higher blood pressure in the glomerular capillaries increases filtration, while lower pressure decreases filtration.
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Figure 17-7
Filter selectivity.
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Figure 17-8
Comparison of damaged and healthy kidneys.
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Control of Filtration
• Changes in blood pressure change filtration rate.
– Minor changes in systolic blood pressure do not change glomerular pressure because it is protected by a mechanism called autoregulation.
As systemic BP increases, the afferent arterioles leading into the glomerulus constrict, decreasing the amount of blood getting into the glomerulus.
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Control of Filtration
• Changes in blood pressure change filtration rate.
– Autoregulation can be overridden.
Since the kidney regulates fluid volume, the kidney can work with the cardiovascular system to regulate blood pressure. Glomerular filtration can decrease to conserve fluid when blood pressure falls, or increase filtration if blood pressure rises. The sympathetic nervous system can control urine production through the adrenal medulla.
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Control of Tubular Reabsorption and Secretion
• Tubular reabsorption and secretion control the chemistry and volume of urine.
– Substances that are reabsorbed move from the tubule back to the blood stream via the peritubular capillaries and stay in the body. – Substances that are secreted stay in the tubule and eventually leave the body via the urine.
• Anything that affects reabsorption and secretion affects urine chemistry.
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Control of Tubular Reabsorption and Secretion
• The first thing that affects tubular reabsorption and secretion is tubule permeability.
– Each section of the tubule can reabsorb and secrete different substances. – Molecules move across membranes through several different methods including diffusion and active transport. (remember transport methods?) – Differences in tubular permeability result in dramatic differences in what molecules are reabsorbed or secreted in each part of the tubule.
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Table 17-2
Individual Tubule Functions.
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Clinical Application: Kidney Stones
• Kidney stones:
– when substances in the urine crystallize in the renal tubule, – often because the concentration of the molecule is higher than normal. – cause of stones is frequently a mystery
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Clinical Application: Kidney Stones
• Stones can be made of:
– calcium, uric acid – caused by kidney infections.
• Some people are more susceptible than others.
– some stones pass unnoticed, – while others that are larger or irregularly shaped may lodge in the tubule, obstructing flow and irritating nearby tissues.
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Clinical Application: Kidney Stones
• Symptoms include: 1.blood in the urine 2.severe flank pain. • Stones may move on their own • May be treated with increased fluid intake,
– Lithotripsy (shock waves to break the stone), or surgery if these don’t work. – Patients are asked to filter their urine to look for the passage of these stones, some as small as sand.
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Figure 17-9
Sites of tubular reabsorption and secretion.
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Applied Science: Electrolyte and Acid Balance
• The kidney maintains electrolyte balance by selectively excreting or reabsorbing electrolytes within the tubular system. • The relationship between hydrogen ions (H+) and bicarbonate ions (HCO3) determines the blood pH (level of acidity or alkalinity). This is called the acid/base relationship.
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Applied Science: Electrolyte and Acid Balance
• If too much acid is present, H+ will be excreted to a greater level in the urine and more bicarbonate ions will be reabsorbed. • The respiratory system also plays a role by blowing off more carbon dioxide, which is an acid.
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Control of Tubular Reabsorption and Secretion
• The third factor that affects reabsorption and secretion are several hormones that regulate blood pressure.
– Antidiuretic Hormone – Aldosterone – Atrial Natriuretic Peptide – Renin-Angiotensin-Aldosterone
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Control of Tubular Reabsorption and Secretion
• Antidiuretic hormone (ADH) is made by the hypothalamus and secreted from the posterior pituitary when BP decreases or ionic concentration increases.
ADH increases permeability of distal tubules and the collecting duct. More water is reabsorbed, increasing blood volume, increasing blood pressure, and diluting the ionic concentration. Less urine is produced. Alcohol or caffeine inhibit ADH production, increasing urine production.
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Control of Tubular Reabsorption and Secretion
• Aldosterone is an adrenocorticosteroid secreted by the adrenal cortex.
Secreted when plasma sodium decreases or plasma potassium increases. Increases the reabsorption of sodium ions and secretion of potassium ions
• – increasing serum sodium levels and decreasing serum potassium levels – by the distal tubule and ascending limb of the nephron loop.
As sodium is reabsorbed, water is also reabsorbed, decreasing urine volume.
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Control of Tubular Reabsorption and Secretion
• Atrial natriuretic peptide (ANP) is secreted by the atria of the heart when blood volume increases.
ANP decreases sodium reabsorption and thus increases urination. Sodium pulls water with it
• If you pee off more NA, more water will follow it
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The Urinary Bladder and Urination Reflex
• Glomerular filtrate flows out the collecting duct, into the minor calyces, and then into the major calyces, forming the renal pelvis. • Once the glomerular filtrate leaves the collecting ducts, its concentration can’t be changed
– it is now urine
• Urine collects in the renal pelvis and flows down the ureters to the urinary bladder, where it is stored.
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Urinary Bladder
• The urinary bladder is a small hollow organ posterior to the pubic symphysis and behind the peritoneum.
– Lined with transitional epithelium, the only epithelium stretchy enough to expand as the bladder fills. – Ability to stretch is enhanced by a series of pleats called rugae. – Bladder has a muscular wall consisting of several layers of circular and longitudinal smooth muscle and is covered by connective tissue and parietal peritoneum.
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Figure 17-10
The urinary bladder.
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Urination Reflex
• As urine accumulates, the bladder fills and stretches.
– This stretch triggers the urinary reflex and the need to void to empty the bladder. – Urination had been thought to be a spinal reflex, but new research indicates it is controlled by the brain. – When the bladder is full, signals are sent from the bladder to the spinal cord to the pons. – The pons sends parasympathetic signals down the spinal cord, causing contraction of the muscular walls of the bladder, and the bladder empties.
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Urination
• Urine leaves the bladder via the urethra, a thin muscular tube lined with several different types of epithelium along its length.
– Part of your brain can inhibit urination by controlling the internal urethral sphincter, a valve at the junction of the bladder and the urethra, and the external urethral sphincter, a valve that is part of the muscles of the pelvic floor.
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Urination
– Sympathetic stimulation of these sphincters prevents urine from leaving the body. – Although you have little control over bladder contraction, you have good control over the sphincters starting from age 2, or slightly later in boys.
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Figure 17-11
Control of urination.
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Classroom Response System
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The bilateral structure(s) in the urinary system consist of:
a. b. c. d. Bladder Ureter and kidney Urethra All of the above
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The bilateral structure(s) in the urinary system consist of:
a. b. c. d. Bladder Ureter and kidney Urethra All of the above
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The processes necessary to make urine are:
a. b. c. d. Contraction, relaxation and expansion Flexion, extension and circumduction Filtration, reabsorbtion, and secretion None of the above
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The processes necessary to make urine are:
a. b. c. d. Contraction, relaxation and expansion Flexion, extension and circumduction Filtration, reabsorbtion, and secretion None of the above
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Blood supply is brought to the renal hilum of the kidneys via:
a. b. c. d. Renal capsule Renal veins Renal arteries Aorta
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Blood supply is brought to the renal hilum of the kidneys via:
a. b. c. d. Renal capsule Renal veins Renal arteries Aorta
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The following is NOT a region of the kidney:
a. b. c. d. Renal cortex Renal medulla Renal pelvis Renal saddle
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The following is NOT a region of the kidney:
a. b. c. d. Renal cortex Renal medulla Renal pelvis Renal saddle
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The collecting tubules for the urine that is formed in the kidney are found in the:
a. b. c. d. Renal pyramids Renal columns Major calyces Minor calyces
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The collecting tubules for the urine that is formed in the kidney are found in the:
a. b. c. d. Renal pyramids Renal columns Major calyces Minor calyces
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The glomerulus is actually:
a. b. c. d.
A part of the bladder A type of neoplasm The name for the filtrating system A ball of capillaries
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The glomerulus is actually:
a. b. c. d.
A part of the bladder A type of neoplasm The name for the filtrating system A ball of capillaries
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The main functional unit of the kidney is the:
a. b. c. d. Renal nephron Renal pelvis Tubules Renal calculi
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The main functional unit of the kidney is the:
a. b. c. d. Renal nephron Renal pelvis Tubules Renal calculi
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The Loop of Henle consists of:
a. b. c. d.
The proximal tubule The descending and ascending loop The collecting tubules The ascending loop
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The Loop of Henle consists of:
a. b. c. d.
The proximal tubule The descending and ascending loop The collecting tubules The ascending loop
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These blood vessels carry blood into the glomerulus
a. b. c. d. Efferent arterioles Afferent arterioles Peritubular capillaries Corticle Radiate arteries
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These blood vessels carry blood into the glomerulus
a. b. c. d. Efferent arterioles Afferent arterioles Peritubular capillaries Corticle Radiate arteries
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Which of the following are considered metabolic waste?
a. b. c. d. Urea and creatinine Glomerular filtrate Oxygen Glucose
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Which of the following are considered metabolic waste?
a. b. c. d. Urea and creatinine Glomerular filtrate Oxygen Glucose
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Autoregulation is:
a. b. c. d.
Utilized in bladder control Controlled nephron division Adjustment for minor blood pressure changes The amount of urine passing through the ureters
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Autoregulation is:
a. Utilized in bladder control b. Controlled nephron division c. Adjustment for minor blood pressure changes d. The amount of urine passing through the ureters
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Angiotensin I is converted to angiotensin II by:
a. b. c. d. Renin Angiotensinogen Aldosterone ACE
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Angiotensin I is converted to angiotensin II by:
a. b. c. d. Renin Angiotensinogen Aldosterone ACE
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The following is a hormone secreted by the kidney:
a. b. c. d. Antidiuretic hormone Aldosterone Atrial natriuretic peptide None of the above
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The following is a hormone secreted by the kidney:
a. b. c. d. Antidiuretic hormone Aldosterone Atrial natriuretic peptide None of the above
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Urinary control occurs in the:
a. b. c. d.
Kidney Bladder Brain Sphincters
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Urinary control occurs in the:
a. b. c. d.
Kidney Bladder Brain Sphincters
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Diabetes insipidus is an endocrine disorder characterized by:
a. b. c. d. High levels of ADH Decrease in urine output High levels of urine output No change in urine output
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Diabetes insipidus is an endocrine disorder characterized by:
a. b. c. d. High levels of ADH Decrease in urine output High levels of urine output No change in urine output
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In a healthy urinary system, urine:
a. b. c. d.
Contains urea Is sterile Has no protein or glucose All of the above
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In a healthy urinary system, urine:
a. b. c. d.
Contains urea Is sterile Has no protein or glucose All of the above
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Contractions of the urinary bladder are:
a. b. c. d.
Voluntarily controlled Involuntary Triggered by sympathetic output Caused by the urinary bladder emptying
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Contractions of the urinary bladder are:
a. b. c. d.
Voluntarily controlled Involuntary Triggered by sympathetic output Caused by the urinary bladder emptying
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Second Edition
CHAPTER
17
The Urinary System: Filtration and Fluid Balance
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
Learning Objectives
• Identify the parts of the urinary system. • Explain general functions of the urinary system. • Explain the relationships of the urinary system to the endocrine & circulatory systems. • Describe the structure & function of the nephron
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
Learning Objectives
• Compare urinary system of the male with the female urinary system. • Identify the constituents of urine. • Differentiate processes of secretion, filtration, and reabsorption & where they occur in the nephron.
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
Introduction
• The urinary system acts as a purification plant, cleaning the blood of waste materials. • Urinary system controls electrolyte and fluid balances for your body. • Kidneys filter blood, reabsorb and secrete ions, and produce urine.
– Without this important function you would die in a few days.
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
System Overview
• Consists of:
– 2 kidneys; bean-shaped organs located in the superior dorsal abdominal cavity that filter blood and make urine – Accessory structures – Ureter is a tube that carries urine from each kidney to – The single urinary bladder, located in the inferior ventral pelvic cavity.
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
System Overview
• Bladder is basically an expandable sac • Urethra is the tube that transports urine from the bladder to the outside of the body. • The job of the urinary system is to make urine, thereby controlling:
– the body’s fluid and electrolyte balance – eliminating waste products
Copyright ©2011 by Pearson Education, Inc. All rights reserved.
System Overview
• To make urine, 3 processes are necessary:
– Filtration – filtering the blood. What passes through the filter is called a filtrate. – Reabsorption – substances stay in the body after being removed from urine – Secretion – substances move from the blood stream and leave the body in the urine
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Figure 17-1
Anatomy of the urinary system.
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External Anatomy of the Kidney
• The kidney is covered by a fibrous layer of connective tissue called the renal capsule.
– Part that gives the kidney it’s bean shape is called the renal hilum.
• At the hilum
– renal arteries bring blood to the kidneys to be filtered – renal veins take the filtered blood away from the kidney. – The ureter is also attached at the hilum to transport urine from the kidney to the bladder.
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Internal Anatomy of the Kidney
• The kidney can be divided into 3 layers:
– Renal cortex – outer layer –this is where blood filtration occurs – Renal medulla – middle layer – contains a number of triangle-shaped, striped areas called renal pyramids
Composed of collecting tubules for the urine that is formed in the kidney
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Internal Anatomy of the Kidney
• The kidney can be divided into 3 layers:
– Renal pelvis – inner layer – a funnel, divided into 2 or 3 large collecting cups called major calyces.
Each major calyx is divided into several minor calyces, forming cup-shaped areas around the tips of the pyramids.
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Internal Anatomy of Kidney
• The blood is filtered by millions of tiny filters in the cortex, • Filtrate flows through tiny tubules in the medulla and collects in the renal pelvis. • Renal pelvis, the enlarged proximal portion of the ureter, empties into the ureter where urine is carried to the bladder.
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Figure 17-2
The internal and external anatomy of the kidney.
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Internal Anatomy of Kidney
• Blood vessels
– Good blood supply to the kidney is essential – A single renal artery enters each kidney at the hilum, branching into 5 segmental arteries. – The segmental arteries branch into lobar arteries in the renal sinus.
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The Nephron
• The functional unit of the kidney is the nephron, consisting of millions of microscopic funnels and tubules. • The nephron can be divided into two distinct parts:
– The renal corpuscle – a filter – The renal tubule – where reabsorption and secretion take place
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Renal Corpuscle
• Blood enters the renal corpuscle via the glomerulus, a ball of capillaries. • Surrounding the glomerulus is a doublelayered membrane called the glomerular capsule, or Bowman’s capsule.
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Renal Corpuscle
• Blood flows into the glomerulus and everything BUT blood cells and a few large molecules, mainly protein, are pushed from the capillaries across the filter and into the glomerular capsule. • The material filtered from the blood into the glomerular capsule is called glomerular filtrate. • If blood or protein leaks into urine it can indicate a kidney filtration problem.
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Figure 17-4
The nephron.
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Renal Tubule
• The rest of the nephron is a series of tubes known as renal tubules. • Glomerular filtrate travels from the glomerular capsule into the first part of the renal tubule, the proximal tubule.
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Renal Tubule
• From the proximal tubule, glomerular filtrate flows into the nephron loop (or the Loop of Henle).
– The nephron loop consists of the descending loop (similar in structure to the proximal tubule) and the ascending loop
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Renal Tubule
• Glomerular filtrate travels from the nephron loop to the distal tubule.
– The wall of the distal tubule is like that of the ascending branch of the nephron loop. – From the distal tubule, glomerular filtrate flows into one of several collecting ducts
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Renal Tubule
• The collecting ducts lead to minor calyces, then to major calyces, the renal pelvis, and the ureter. • At this point, the glomerular filtrate is urine.
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Figure 17-5
A functional renal unit.
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Renal Tubule
• Blood vessels are in close proximity to the nephrons because substances move between the tubules and the bloodstream.
– Blood approaches the nephron via the afferent arteriole. – Blood flows from the afferent arteriole into the glomerulus. – Blood flows from the glomerulus via the efferent arteriole into the peritubular capillaries and vasa recta.
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Renal Tubule
• Blood vessels are in close proximity to the nephrons because substances move between the tubules and the bloodstream.
– These surrounding blood vessels allow for reabsorption and secretion. – Blood leaves the nephron via the cortical radiate veins.
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Clinical Application: Trauma, Ischemia, and Kidney Damage
• The kidney is well vascularized, with each nephron surrounded by blood vessels. • The flow of blood is controlled by the afferent arteriole. • When blood flow decreases for a period of time, oxygen delivery to the nephron decreases and ischemia results.
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Clinical Application: Trauma, Ischemia, and Kidney Damage
• Blood flow can be decreased by any number of hormonal mechanisms causing prolonged vasoconstriction, such as severe blood loss. • If the situation continues long enough, the tissues will become ischemic and eventually die, causing kidney failure that can be temporary or permanent.
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Urine Formation
• The kidney controls fluid and electrolyte balance by controlling urine volume and composition. • In order to form urine, the nephron must perform three processes:
– Glomerular filtration – Tubular reabsorption – Tubular secretion
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Filtration
• During glomerular filtration, fluid and molecules pass from the glomerular capillaries into the glomerular capsule.
– Across a filter composed of the walls of the capillaries and the podocytes of the glomerular capsule – The filtrate flows into the renal tubule where the chemistry is controlled by reabsorption and secretion – Filtration moves fluid and chemicals into the nephron from blood – Glomerular filtrate is chemically similar to blood
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Reabsorption and Secretion
• Urine is chemically different from plasma because reabsorption and secretion control the concentration of chemicals and volume of urine.
– Substances that are reabsorbed pass from the renal tubule into the peritubular capillaries and return to the blood stream. – Substances that are secreted pass through the peritubular capillaries into the renal tubule and eventually leave the body as urine. – Some substances, like glucose, are completely reabsorbed while substances like metabolic waste products (urea and creatinine) are almost completely secreted as urine.
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Figure 17-6
The processes involved in urine formation.
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Table 17-1
Kidney Fluid Chemistry.
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Control of Filtration
• Filtration is controlled by several factors.
– Filter size – determines what gets through the filter
Podocytes and capillary walls of the renal corpuscle create a filter with fixed openings. Plasma, and many of the substances dissolved in plasma, pass through the filter, but blood cells, platelets, and large molecules, can’t get into a healthy kidney.
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Control of Filtration
• Filtration is controlled by several factors.
– Pressure
Higher pressure on one side of the filter allows chemicals to be pushed though the filter more quickly. Higher blood pressure in the glomerular capillaries increases filtration, while lower pressure decreases filtration.
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Figure 17-7
Filter selectivity.
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Figure 17-8
Comparison of damaged and healthy kidneys.
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Control of Filtration
• Changes in blood pressure change filtration rate.
– Minor changes in systolic blood pressure do not change glomerular pressure because it is protected by a mechanism called autoregulation.
As systemic BP increases, the afferent arterioles leading into the glomerulus constrict, decreasing the amount of blood getting into the glomerulus.
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Control of Filtration
• Changes in blood pressure change filtration rate.
– Autoregulation can be overridden.
Since the kidney regulates fluid volume, the kidney can work with the cardiovascular system to regulate blood pressure. Glomerular filtration can decrease to conserve fluid when blood pressure falls, or increase filtration if blood pressure rises. The sympathetic nervous system can control urine production through the adrenal medulla.
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Control of Tubular Reabsorption and Secretion
• Tubular reabsorption and secretion control the chemistry and volume of urine.
– Substances that are reabsorbed move from the tubule back to the blood stream via the peritubular capillaries and stay in the body. – Substances that are secreted stay in the tubule and eventually leave the body via the urine.
• Anything that affects reabsorption and secretion affects urine chemistry.
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Control of Tubular Reabsorption and Secretion
• The first thing that affects tubular reabsorption and secretion is tubule permeability.
– Each section of the tubule can reabsorb and secrete different substances. – Molecules move across membranes through several different methods including diffusion and active transport. (remember transport methods?) – Differences in tubular permeability result in dramatic differences in what molecules are reabsorbed or secreted in each part of the tubule.
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Table 17-2
Individual Tubule Functions.
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Clinical Application: Kidney Stones
• Kidney stones:
– when substances in the urine crystallize in the renal tubule, – often because the concentration of the molecule is higher than normal. – cause of stones is frequently a mystery
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Clinical Application: Kidney Stones
• Stones can be made of:
– calcium, uric acid – caused by kidney infections.
• Some people are more susceptible than others.
– some stones pass unnoticed, – while others that are larger or irregularly shaped may lodge in the tubule, obstructing flow and irritating nearby tissues.
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Clinical Application: Kidney Stones
• Symptoms include: 1.blood in the urine 2.severe flank pain. • Stones may move on their own • May be treated with increased fluid intake,
– Lithotripsy (shock waves to break the stone), or surgery if these don’t work. – Patients are asked to filter their urine to look for the passage of these stones, some as small as sand.
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Figure 17-9
Sites of tubular reabsorption and secretion.
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Applied Science: Electrolyte and Acid Balance
• The kidney maintains electrolyte balance by selectively excreting or reabsorbing electrolytes within the tubular system. • The relationship between hydrogen ions (H+) and bicarbonate ions (HCO3) determines the blood pH (level of acidity or alkalinity). This is called the acid/base relationship.
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Applied Science: Electrolyte and Acid Balance
• If too much acid is present, H+ will be excreted to a greater level in the urine and more bicarbonate ions will be reabsorbed. • The respiratory system also plays a role by blowing off more carbon dioxide, which is an acid.
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Control of Tubular Reabsorption and Secretion
• The third factor that affects reabsorption and secretion are several hormones that regulate blood pressure.
– Antidiuretic Hormone – Aldosterone – Atrial Natriuretic Peptide – Renin-Angiotensin-Aldosterone
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Control of Tubular Reabsorption and Secretion
• Antidiuretic hormone (ADH) is made by the hypothalamus and secreted from the posterior pituitary when BP decreases or ionic concentration increases.
ADH increases permeability of distal tubules and the collecting duct. More water is reabsorbed, increasing blood volume, increasing blood pressure, and diluting the ionic concentration. Less urine is produced. Alcohol or caffeine inhibit ADH production, increasing urine production.
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Control of Tubular Reabsorption and Secretion
• Aldosterone is an adrenocorticosteroid secreted by the adrenal cortex.
Secreted when plasma sodium decreases or plasma potassium increases. Increases the reabsorption of sodium ions and secretion of potassium ions
• – increasing serum sodium levels and decreasing serum potassium levels – by the distal tubule and ascending limb of the nephron loop.
As sodium is reabsorbed, water is also reabsorbed, decreasing urine volume.
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Control of Tubular Reabsorption and Secretion
• Atrial natriuretic peptide (ANP) is secreted by the atria of the heart when blood volume increases.
ANP decreases sodium reabsorption and thus increases urination. Sodium pulls water with it
• If you pee off more NA, more water will follow it
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The Urinary Bladder and Urination Reflex
• Glomerular filtrate flows out the collecting duct, into the minor calyces, and then into the major calyces, forming the renal pelvis. • Once the glomerular filtrate leaves the collecting ducts, its concentration can’t be changed
– it is now urine
• Urine collects in the renal pelvis and flows down the ureters to the urinary bladder, where it is stored.
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Urinary Bladder
• The urinary bladder is a small hollow organ posterior to the pubic symphysis and behind the peritoneum.
– Lined with transitional epithelium, the only epithelium stretchy enough to expand as the bladder fills. – Ability to stretch is enhanced by a series of pleats called rugae. – Bladder has a muscular wall consisting of several layers of circular and longitudinal smooth muscle and is covered by connective tissue and parietal peritoneum.
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Figure 17-10
The urinary bladder.
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Urination Reflex
• As urine accumulates, the bladder fills and stretches.
– This stretch triggers the urinary reflex and the need to void to empty the bladder. – Urination had been thought to be a spinal reflex, but new research indicates it is controlled by the brain. – When the bladder is full, signals are sent from the bladder to the spinal cord to the pons. – The pons sends parasympathetic signals down the spinal cord, causing contraction of the muscular walls of the bladder, and the bladder empties.
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Urination
• Urine leaves the bladder via the urethra, a thin muscular tube lined with several different types of epithelium along its length.
– Part of your brain can inhibit urination by controlling the internal urethral sphincter, a valve at the junction of the bladder and the urethra, and the external urethral sphincter, a valve that is part of the muscles of the pelvic floor.
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Urination
– Sympathetic stimulation of these sphincters prevents urine from leaving the body. – Although you have little control over bladder contraction, you have good control over the sphincters starting from age 2, or slightly later in boys.
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Figure 17-11
Control of urination.
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Classroom Response System
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The bilateral structure(s) in the urinary system consist of:
a. b. c. d. Bladder Ureter and kidney Urethra All of the above
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The bilateral structure(s) in the urinary system consist of:
a. b. c. d. Bladder Ureter and kidney Urethra All of the above
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The processes necessary to make urine are:
a. b. c. d. Contraction, relaxation and expansion Flexion, extension and circumduction Filtration, reabsorbtion, and secretion None of the above
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The processes necessary to make urine are:
a. b. c. d. Contraction, relaxation and expansion Flexion, extension and circumduction Filtration, reabsorbtion, and secretion None of the above
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Blood supply is brought to the renal hilum of the kidneys via:
a. b. c. d. Renal capsule Renal veins Renal arteries Aorta
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Blood supply is brought to the renal hilum of the kidneys via:
a. b. c. d. Renal capsule Renal veins Renal arteries Aorta
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The following is NOT a region of the kidney:
a. b. c. d. Renal cortex Renal medulla Renal pelvis Renal saddle
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The following is NOT a region of the kidney:
a. b. c. d. Renal cortex Renal medulla Renal pelvis Renal saddle
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The collecting tubules for the urine that is formed in the kidney are found in the:
a. b. c. d. Renal pyramids Renal columns Major calyces Minor calyces
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The collecting tubules for the urine that is formed in the kidney are found in the:
a. b. c. d. Renal pyramids Renal columns Major calyces Minor calyces
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The glomerulus is actually:
a. b. c. d.
A part of the bladder A type of neoplasm The name for the filtrating system A ball of capillaries
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The glomerulus is actually:
a. b. c. d.
A part of the bladder A type of neoplasm The name for the filtrating system A ball of capillaries
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The main functional unit of the kidney is the:
a. b. c. d. Renal nephron Renal pelvis Tubules Renal calculi
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The main functional unit of the kidney is the:
a. b. c. d. Renal nephron Renal pelvis Tubules Renal calculi
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The Loop of Henle consists of:
a. b. c. d.
The proximal tubule The descending and ascending loop The collecting tubules The ascending loop
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The Loop of Henle consists of:
a. b. c. d.
The proximal tubule The descending and ascending loop The collecting tubules The ascending loop
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These blood vessels carry blood into the glomerulus
a. b. c. d. Efferent arterioles Afferent arterioles Peritubular capillaries Corticle Radiate arteries
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These blood vessels carry blood into the glomerulus
a. b. c. d. Efferent arterioles Afferent arterioles Peritubular capillaries Corticle Radiate arteries
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Which of the following are considered metabolic waste?
a. b. c. d. Urea and creatinine Glomerular filtrate Oxygen Glucose
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Which of the following are considered metabolic waste?
a. b. c. d. Urea and creatinine Glomerular filtrate Oxygen Glucose
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Autoregulation is:
a. b. c. d.
Utilized in bladder control Controlled nephron division Adjustment for minor blood pressure changes The amount of urine passing through the ureters
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Autoregulation is:
a. Utilized in bladder control b. Controlled nephron division c. Adjustment for minor blood pressure changes d. The amount of urine passing through the ureters
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Angiotensin I is converted to angiotensin II by:
a. b. c. d. Renin Angiotensinogen Aldosterone ACE
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Angiotensin I is converted to angiotensin II by:
a. b. c. d. Renin Angiotensinogen Aldosterone ACE
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The following is a hormone secreted by the kidney:
a. b. c. d. Antidiuretic hormone Aldosterone Atrial natriuretic peptide None of the above
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The following is a hormone secreted by the kidney:
a. b. c. d. Antidiuretic hormone Aldosterone Atrial natriuretic peptide None of the above
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Urinary control occurs in the:
a. b. c. d.
Kidney Bladder Brain Sphincters
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Urinary control occurs in the:
a. b. c. d.
Kidney Bladder Brain Sphincters
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Diabetes insipidus is an endocrine disorder characterized by:
a. b. c. d. High levels of ADH Decrease in urine output High levels of urine output No change in urine output
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Diabetes insipidus is an endocrine disorder characterized by:
a. b. c. d. High levels of ADH Decrease in urine output High levels of urine output No change in urine output
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In a healthy urinary system, urine:
a. b. c. d.
Contains urea Is sterile Has no protein or glucose All of the above
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In a healthy urinary system, urine:
a. b. c. d.
Contains urea Is sterile Has no protein or glucose All of the above
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Contractions of the urinary bladder are:
a. b. c. d.
Voluntarily controlled Involuntary Triggered by sympathetic output Caused by the urinary bladder emptying
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Contractions of the urinary bladder are:
a. b. c. d.
Voluntarily controlled Involuntary Triggered by sympathetic output Caused by the urinary bladder emptying
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